Add AF_VSOCK support

[stefano-garzarella]

The VSOCK address family facilitates communication between virtual machines and the host they are running on.
AF_VSOCK currently support STREAM, SEQPACKET. DGRAM support is WiP.

The addressing is formed by 2 integers: <CID, port>

• CID: Context ID, it is the ID assigned to the VM
  0, 1, 2 CIDs are reserved:
  0 - hypervisor CID (rarely used)
  1 - local communication (loopback)
  2 - host CID (the guest can always reach the host using CID=2)

• port: port number on 32bit to reach a specific process

Added also tests using the vsock_loopback kernel module on a single host.
This module (Linux v5.8+) allows to use AF_VSOCK on a single host, without spawning a VM.

Other info and examples of AF_VSOCK (socat, iperf, python, etc.) are summarized in this 2 talks:

• https://stefano-garzarella.github.io/posts/2021-01-22-socat-vsock/
• https://stefano-garzarella.github.io/posts/2020-02-20-vsock-nested-vms-loopback/

[realneel]

@stefano-garzarella Thanks for the PR.

@tuexen Do you have some time to review this?

[tuexen]

@stefano-garzarella Thanks for the PR.

@tuexen Do you have some time to review this?

I can take a look at it next week or so, but I'm no familiar with Linux and VSOCK in particular.

[ldoktor]

Thanks @stefano-garzarella for adding the support for vsock to uperf I mean to use it in our testing. I gave it a quick functional try and following setup worked well for me:

• created a F33-based following the steps from your example: https://stefano-garzarella.github.io/posts/2021-01-22-socat-vsock/
• deployed this version of uperf on both, the guest and host
• ran ./uperf -s -v -S vsock -P20000 in guest
• ran h=42 ./uperf -v -S vsock -m ../workloads/vsock.xml on host

Note the opposite direction (running -s on host) failed with 2 says: Error creating ports: Interrupted system call (full details sent directly to Stefano) so beware of this limitation while reviewing this PR. Anyway function-wise this PR seems to work well for me and I am really interested in getting this to the mainline.

[stefano-garzarella]

@ldoktor thanks for testing and reporting the issues.

Note the opposite direction (running -s on host) failed with 2 says: Error creating ports: Interrupted system call (full details sent directly to Stefano) so beware of this limitation while reviewing this PR. Anyway function-wise this PR seems to work well for me and I am really interested in getting this to the mainline.

I should fixed this one, the problem was that vsock uses unsigned int port numbers, so uperf can fail with "Error creating ports:" error message also if everything is fine.
The last commit of this PR should fix the issues checking UPERF_FAILURE (-1) instead of negative return value for p->listen(). This should work well, since we always return that value on failure and vsock ports -1 is reserved (VMADDR_PORT_ANY).

[ldoktor]

@stefano-garzarella thank you, this version seem to address the issue mentioned earlier.

[realneel]

Looks good to me

[stefano-garzarella]

@tuexen thanks for the review! I just pushed the fixes.

[tuexen]

Merged. Thanks for addressing my issues.